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How many stages of life are there? According to Hindu teachings, human life unfolds in four stages: childhood, apprenticeship, adulthood and old age. William Shakespeare in As You Like It insisted on seven, beginning with infancy, when we are “mewling and puking,” and ending with old age, when we are “sans teeth, sans eyes, sans taste, sans everything.”

It will come as no surprise that social scientists have expressed their own opinions on the matter, often arguing over the details and sometimes specifying different sets of stages for different abilities, such as cognitive development (Jean Piaget), moral reasoning (Lawrence Kohlberg) and psychosexual development (Sigmund Freud). What is more, when cultures change sufficiently to alter behavior during certain age spans, social scientists sometimes add >new stages as they notice them.